Dilation of the annulus of the mitral valve prevents the valve leaflets from fully coapting when the valve is closed. Regurgitation of blood from the ventricle into the atrium results in increased total stroke volume and decreased cardiac output, and ultimate weakening of the ventricle secondary to a volume overload and a pressure overload of the atrium. Dilation of the annulus is sometimes treated by implanting a prosthetic mitral valve at a patient's native mitral valve.